Short Circuit Current Ratings Calculation and Tools · Manufacturer Name: ABC Company Voltage:...
Transcript of Short Circuit Current Ratings Calculation and Tools · Manufacturer Name: ABC Company Voltage:...
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Copyright © 2018 Rockwell Automation, Inc. All Rights Reserved. 1
CT432Short Circuit Current Ratings
Calculation and Tools
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Agenda
Summary
Additional Design Tools
Evaluating Panel SCCR
Overview
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Overview
Why Understanding SCCR is Important
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Importance of Short-Circuit Current Ratings
Short-Circuit:
An overcurrent fault that exceeds normal full load currents... 10x, 100x, 1,000x of FLC
Catastrophic results if SC Faults are not cleared properly
SC Faults are critical to:
Worker safety
Customer applications (critical care, continuous process)
Circuit components, assemblies and system Installations
Productivity and downtime ($100k’s per hour)
We forget how much “power” we are really discussing:
“65kA @ 400V”
“100kA @ 480V”
“80kA @ 690V”
Recent changes to NEC and UL have mandated for a wider range of electrical panels to be marked with the Short Circuit Current Rating (SCCR) of the panel.
Local inspectors are having to more strictly enforce that the SCCR rating of a panel Meets or Exceeds the available fault current where it is connected.
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Normal Load Current Short Circuit Current
Cu
rren
t (A
)
Available Short Circuit Current (Ipa)
Time
Clearing Time (tc)
Peak Let-Thru (Ipl)
Let-Thru (I2t)
Non-Current Limiting
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Evaluating Panel SCCR
The Steps
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What is a Short-Circuit Current Rating?
Short-Circuit “Interrupting Rating” (Breaking Capacity): The maximum short circuit current at rated voltage that an overcurrent protective device can
safely interrupt and clear (fuses and circuit breakers)
Short-Circuit Current Rating – SCCR: The maximum available short-circuit current an electrical component can sustain without the
occurrence of excessive damage when protected with an overcurrent protective device
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“Motor Protection Circuit Breaker”
Protective Device
Icu/Ics = 65kA @ 400V
“Combination Motor Controllers”
Icu/Ics = 65kA @ 400V
IEC Type “2” Coordination
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Building a Short-Circuit Current Rating
Protection Levels: Component
Combinations
Branch circuit
Panel Assembly
“Motor Protection Circuit Breaker”
Icu/Ics = 65kA @ 400V
“Combination Motor Controllers”
Icu/Ics = 65kA @ 400V
IEC Type “2” Coordination
“Panel SCCR”
65kA @ 400V
“Branch circuit SCCR”
65kA @ 400V
Manufacturer Name: ABC Company
Voltage: _480V_ Phase: _3 Phase_ Frequency: _60 Hz_
Full Load Current: 300 Amperes
Short Circuit Current Rating * : 65,000A
Maximum Circuit Breaker Rating: 400A * Suitable for use on a circuit capable of delivering not more than
65,000 symmetrical amperes of short-circuit current.
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Common Global SCCR Requirements
V
Utility
35kA AFC
Main Switchgear
MCB1
F1
48kA AFC
14kA AFCX X
X
X 22kA AFC
Manufacturer Name: ABC Company
Voltage: _480V_ Phase: _3 Phase_ Frequency: _60 Hz_
Full Load Current: 300 Amperes
Short Circuit Current Rating * : 65,000A
Maximum Circuit Breaker Rating: 400A * Suitable for use on a circuit capable of delivering not more than
65,000 symmetrical amperes of short-circuit current.
Manufacturer Name: ABC Company
Voltage: _480V_ Phase: _3 Phase_ Frequency: _60 Hz_
Full Load Current: 300 Amperes
Short Circuit Current Rating * : 65,000A
Maximum Circuit Breaker Rating: 400A * Suitable for use on a circuit capable of delivering not more than
65,000 symmetrical amperes of short-circuit current.
Manufacturer Name: ABC Company
Voltage: _480V_ Phase: _3 Phase_ Frequency: _60 Hz_
Full Load Current: 300 Amperes
Short Circuit Current Rating * : 65,000A
Maximum Circuit Breaker Rating: 400A * Suitable for use on a circuit capable of delivering not more than
65,000 symmetrical amperes of short-circuit current.
Manufacturer Name: ABC Company
Voltage: _480V_ Phase: _3 Phase_ Frequency: _60 Hz_
Full Load Current: 300 Amperes
Short Circuit Current Rating * : 65,000A
Maximum Circuit Breaker Rating: 400A * Suitable for use on a circuit capable of delivering not more than
65,000 symmetrical amperes of short-circuit current.
Determine system voltage and frequency Determine Available Fault Currents (AFC) Ensure control panel SCCR covers the AFC Mark the panels accordingly
SCCR “Evaluation Process” varies greatly
480V, 60 Hz
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UL 508A SBDetermining SCCR - Three Basic Steps
UL 508A Supplement SB Short-Circuit Current Ratings for Industrial Control Panels shall be determined by
the following evaluation procedure:
SB4.1: Short-Circuit Current Rating (SCCR)a) First, establish the short circuit current ratings of individual power circuit
components as specified in SB4.2
b) Second, modify (limit) the available short-circuit current within a portion of a circuit
in the panel due to the presence of current limiting components as specified in
SB4.3
c) Third, determine the overall panel short-circuit current rating as specified in
SB4.4
9
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UL 508A SB4.2Individual Power Circuit Components
SB4.2.1 All power circuit components, including
disconnect switches, branch circuit protective
devices, branch circuit fuse holders, load
controllers, motor overload relays, terminal blocks,
and bus bars, shall have a short-circuit current
rating expressed in amperes or kilo-amperes
and voltage.
Exception No. 1: Power transformers,
reactors, current transformers, dry-type
capacitors, resistors, varistors, and voltmeters
are not required to have a short circuit current
rating.
Exception No. 2: The “S” contactor of a wye-
delta motor controller is not required to have a
short-circuit current rating.
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Motor Starter Coordination
Type 1 Coordination Under short circuit conditions, the contactor or starter shall cause no danger to persons
or installation and may not be suitable for further service without repair and
replacement of parts.
Type 2 Coordination Under short circuit conditions, the contactor or starter shall cause no danger to persons
or installation and shall be suitable for further use. The risk of contact welding is
recognized, in which case the manufacturer shall indicate the measures to be taken in
regards to equipment maintenance.
Type F Coordination Under short circuit conditions, no damage to the motor protection circuit breaker is
permissible. The contactor may be inoperative and require replacement.
Self-Protected Coordination Under short circuit conditions, no damage to the contactor, overload relay, or other parts
is permissible.
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UL 508A SB4.2.2Determining the SC Circuit Rating of Components
SB4.2.2 – The short circuit current rating of a component shall be
established by one of the following methods:
A) – The short circuit current rating marked on the component
or instructions provided with the component.
B) – The short circuit current rating determined by the voltage
rating of the component and the assumed short circuit
current from Table SB4.1; or
C) – The short circuit current rating for a load controller,
motor overload relay, or combination motor controller that
has been investigated in accordance with the performance
requirements, including short circuit test requirements for
standard fault currents or high fault currents specified in the
Standard for Industrial Control Equipment, UL 508, and
described in the manufacturer’s Procedure
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UL 508A SB4.2.2Determining the SC Circuit Rating of Components
http://www.rockwellautomation.com/global/support/global-sccr.page
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UL 508A SB4.2.2Determining the SC Circuit Rating of Components
http://www.rockwellautomation.com/global/support/global-sccr.page
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UL 508A SB4.2.2Determining the SC Circuit Rating of Components
http://www.rockwellautomation.com/global/support/global-sccr.page
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UL 508A SB4.2.2Determining the SC Circuit Rating of Components
http://www.rockwellautomation.com/global/support/global-sccr.page
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UL 508A SB4.2.2Determining the SC Circuit Rating of Components
http://www.rockwellautomation.com/global/support/global-sccr.page
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UL 508A SB4.2.2Determining the SC Circuit Rating of Components
http://www.rockwellautomation.com/global/support/global-sccr.page
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UL 508A SB4.2.2Determining the SC Circuit Rating of Components
http://www.rockwellautomation.com/global/support/glo
bal-sccr.page
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UL 508A SB4.2.2Determining the SC Circuit Rating of Components
http://www.rockwellautomation.com/global/support/glo
bal-sccr.page
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UL 508A SB4.3Feeder Devices that Limit SC Current
SB4.3 – Feeder components that limit the short-circuit current available:
SB4.3.1 – For branch circuits supplied by a power transformer with an
isolated secondary winding…
SB4.3.2 – For branch circuits supplied by a Listed circuit breaker marked
“current limiting” in the feeder circuit…
SB4.3.3 – For branch circuits supplied by a Class CC, G, J, L, RK1, RK5,
or T fuse in the feeder circuit…
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UL 508A SB4.3.1Branch Circuits supplied by a Power Transformer with an Isolated Secondary Wiring
SB4.3.1 A) – For a power transformer with a Marked
or Known impedance…the Secondary Short Circuit
Current (Isc) is calculated using the formulas below… Single Phase Transformers
Transformer FLC (IFL) = Transformer VA / Voltage*
Short Circuit Current (Isc line-to-line) = (Transformer FLC (IFL))/Transformer
Impedance (Z)
*Line-to-line secondary voltage
• Three Phase Transformers
• Transformer FLC (IFL) = Transformer VA / (Voltage** x 1.732)
• Short Circuit Current (Isc line-to-line-to-line) = (Transformer FLC (IFL))/Transformer
Impedance (Z)
• **Line-to-line-to-line secondary voltage
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UL 508A SB4.3.1Branch Circuits supplied by a Power Transformer with an Isolated Secondary Wiring
SB4.3.1 B) – For a power transformer with an Unmarked impedance, or with a Marked
or Known impedance not less than 2.1%, the Secondary Short Circuit Current (Isc)
can be calculated using the formula method or Tables SB4.3 or SB4.4
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UL 508A SB4.3.1Branch Circuits supplied by a Power Transformer with an Isolated Secondary Wiring
SB4.3.1 B) – For a power transformer with an Unmarked impedance, or with a Marked
or Known impedance not less than 2.1%, the Secondary Short Circuit Current (Isc)
can be calculated using the formula method or Tables SB4.3 or SB4.4
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UL 508A SB4.3Current-Limiting Components
SB4.3.2 For branch circuits supplied by a Listed circuit breaker marked “current-limiting” in the feeder circuit, the short-circuit current rating on the line side of the circuit breaker shall be one of the following:
a) The short-circuit current rating of the feeder circuit breaker when all components in the branch circuit have a short-circuit current rating not less than the published peak let-through current of the circuit breaker, see Figure SB4.1, and the short-circuit current rating of all branch circuit protective devices on the load side are not less than the short-circuit current rating of the feeder circuit breaker;
b) The smallest short-circuit current rating of any branch circuit protective device on the load side of the feeder circuit breaker, when the conditions of SB4.3.2(a) exist except the short-circuit current rating of the branch circuit protective devices on the load side are less than the short-circuit current rating of the feeder circuit breaker.
65kA SCC Available
Branch circuit PD65kA SCCR
Motor Controller18kA SCCR
17kA IpLet-through
a) 65kA Panel SCCR
Feeder CB“Current Limiting”
65kA SCCR
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UL 508A SB4.4 Overall SCCR of the Panel
SB4.4.1 For each branch circuit provided with branch circuit protection within the industrial control panel, the smallest short-circuit current rating of all power circuit components on the load side of a branch circuit protective device and the control circuit overcurrent protection in SB3.2.1 shall be determined and compared with the short-circuit current rating of the branch circuit protective device. The smaller of the two ratings shall be assigned to the line side of the branch circuit protective device.
In other words, use the lowest rating of a component or branch protective device to determine branch rating.
65kA
10kA
65kA 70kA
10kA Panel Rating
100kA
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1. Panel SCCR will be determined by the smallest
SCCR of any feeder or branch overcurrent
protective device or component
2. Branch Circuit Protection Devices, BCPDs must
cover panel available fault level
3. All components and controllers with SCCR’s
based on high-fault ratings must be used with
the specified branch circuit protective device
4. And finally, the panel SCCR must cover the
available fault current supplying the panel!
Available Fault Current:40kA @ 480V
Manufacturer Name: ABC Company
Voltage: _480V_ Phase: _3 Phase_ Frequency: _60 Hz_
Full Load Current: 300 Amperes
Short Circuit Current Rating * : 65,000A
Maximum Circuit Breaker Rating: 400A * Suitable for use on a circuit capable of delivering not more than
65,000 symmetrical amperes of short-circuit current.
UL 508A SB4.4 Panel SCCR – Validate Results
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Disconnecting
Means
Connection
Systems
Branch Circuits “Power”
Branch Circuits “Control”
Manufacturer Name: ABC Company
Voltage: _480V_ Phase: _3 Phase_ Frequency: _60 Hz_
Full Load Current: 300 Amperes
Short Circuit Current Rating * : 65,000A
Maximum Circuit Breaker Rating: 400A * Suitable for use on a circuit capable of delivering not more than
65,000 symmetrical amperes of short-circuit current.
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Resources
Additional Design Tools
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Access GSCCR Tool
North American Standards,
Configurations, and Ratings
Global SCCR: PowerFlex® Low
Voltage AC Drives Profile
Global SCCR: IEC Motor Control
Solutions Profile
Global SCCR: SMC™ Soft
StartersGlobal SCCR: NEMA Motor
Control Solutions Profile
Short-Circuit Current
Ratings Profile
Resources
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Additional Design Tools
• MCS Star
• 141A busbar systems
• Industrial Automation Builder (IAB)
• Communication layout and design software
• Safety Automation Builder
• Safety system layout and design software
• Eplan
• Panel layout and design software
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Summary
Rockwell provides multiple tools and resources to help you provide the right product to your customers to achieve their safety and productivity goals
Based on customer’s aversion to machine downtime, starter coordination can be used to better sell to their needs
Knowing available fault current can make design easier and more cost effective
Understanding SCCR can save lives and equipment